Usually found in one breast but can affect both breasts at the same time. The increase in lump size and breast tenderness occurs just before the menstrual cycle and decreases in size and resolution after the menstrual cycle. Having one or more cysts does not increase your risk of breast cancer but may interfere with your ability to detect abnormal changes that may need to be evaluated. The supporting tissue that gives the breast its shape is made up of adipose tissue and fibrous connective tissue. Cysts develop when there is an overgrowth of glands and fibrocystic changes within the milk ducts that cause them to dilate and fill with fluid (Laronga et al.